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      <title>1、Java并发模型与内存模型 - 交互式测验</title>
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          <div class="quiz-container">
            <div class="quiz-header">
              <h1>1、Java并发模型与内存模型 - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
            </div>
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  {
    "question": "根据Java内存模型(JMM)的定义，它的核心目标是什么？",
    "options": [
      "管理Java对象的内存分配和垃圾回收。",
      "定义线程的生命周期状态（如NEW, RUNNABLE, BLOCKED）。",
      "保证多线程环境下共享变量的可见性和操作的有序性。",
      "提供高效的线程池实现，如Executor框架。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "Java内存模型（JMM）的核心在于解决多线程并发时可能出现的两个主要问题：一是某个线程对共享变量的修改，其他线程无法立即看到（可见性）；二是为了优化性能，编译器或处理器可能对指令进行重排序，导致程序执行顺序与代码不一致（有序性）。因此，JMM通过定义一系列规则来保证可见性和有序性。",
    "source": "文档中「3. Java内存模型（JMM）概述」部分",
    "hint": "文档中提到：\"JMM的核心目标是保证不同线程之间的可见性和操作的有序性。\""
  },
  {
    "question": "当一个Java线程因为等待进入一个被其他线程持有的`synchronized`代码块而被阻塞时，它处于哪种状态？",
    "options": [
      "WAITING",
      "BLOCKED",
      "RUNNABLE",
      "TIMED_WAITING"
    ],
    "correctAnswerIndex": 1,
    "explanation": "线程状态`BLOCKED`特指线程在等待获取一个监视器锁（Monitor Lock），也就是等待进入`synchronized`修饰的代码块或方法。而`WAITING`状态通常是由于调用了`Object.wait()`或`LockSupport.park()`等方法，等待其他线程的显式唤醒。",
    "source": "文档中「2. 线程的生命周期与状态转换」部分",
    "hint": "文档中对`BLOCKED`状态的定义是：“线程因为等待锁资源而被阻塞。”"
  },
  {
    "question": "根据文档，`volatile`关键字在Java并发编程中主要提供了哪两项保证？",
    "options": [
      "原子性和互斥性",
      "内存可见性和禁止指令重排序",
      "线程安全性和锁升级",
      "任务窃取和线程池复用"
    ],
    "correctAnswerIndex": 1,
    "explanation": "`volatile`关键字有两个关键作用：1. 保证内存可见性，即当一个线程修改了volatile变量的值，这个新值对其他线程是立即可见的。2. 禁止指令重排序，通过插入内存屏障来防止编译器和处理器为了优化而打乱volatile变量相关的指令执行顺序，从而保证了程序的有序性。",
    "source": "文档中「6. volatile的原理与内存可见性」部分",
    "hint": "在`volatile`的源码分析部分，文档明确指出了“内存可见性”和“禁止重排序”这两点。"
  },
  {
    "question": "文档中提到，`synchronized`关键字背后的实现基于什么机制？",
    "options": [
      "仅基于CPU的CAS（Compare-and-Swap）原子指令。",
      "基于每个Java对象都关联的监视器锁（Monitor Lock）。",
      "基于`volatile`关键字提供的内存屏障。",
      "基于操作系统的信号量（Semaphore）机制。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "Java中的`synchronized`同步机制是建立在监视器锁（Monitor Lock）之上的。每个Java对象都可以作为一个锁。当线程进入`synchronized`代码块时，它必须获取该对象的监视器锁。虽然在锁的优化过程中（如轻量级锁）会用到CAS操作，但其根本机制是监视器锁。",
    "source": "文档中「5. synchronized的实现与锁的机制」部分",
    "hint": "文档中明确指出：“`synchronized`背后的实现基于监视器锁（Monitor Lock）机制，每个对象都有一个锁与之关联。”"
  },
  {
    "question": "为什么在调用对象的 `wait()` 或 `notify()` 方法前，线程必须先持有该对象的监视器锁？",
    "options": [
      "这是Java语法的设计巧合，没有特殊原因。",
      "为了防止多个线程同时调用 `notifyAll()` 导致系统崩溃。",
      "因为`wait()`/`notify()`机制依赖于监视器锁来管理线程的等待和唤醒队列，确保线程间通信的正确性。",
      "为了提高程序的执行性能。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "`wait()`和`notify()`是用于线程间协作的机制，它们必须与锁（即`synchronized`）配合使用。线程调用`wait()`会释放持有的锁并进入等待队列，而调用`notify()`的线程会从等待队列中唤醒一个线程。如果不持有锁就调用，就无法保证线程状态的同步和数据的一致性，可能导致“丢失的唤醒”等问题。因此，这个要求是为了保证线程间通信的原子性和正确性。",
    "source": "文档中「7. 线程间通信：wait/notify机制」部分",
    "hint": "文档中提到：“`wait()`和`notify()`方法依赖于每个对象内置的监视器锁，线程必须持有对象的锁才能调用这些方法。”"
  },
  {
    "question": "Java内存模型(JMM)通过哪种底层技术手段来禁止指令重排序，以保证`volatile`等关键字的有序性语义？",
    "options": [
      "在编译时静态分析代码，重构所有可能的执行路径。",
      "运行时动态增加线程的调度优先级。",
      "在特定的指令前后插入内存屏障（Memory Barrier）。",
      "强制所有操作都在主内存中直接进行，不使用CPU缓存。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "为了实现`volatile`和`synchronized`的内存语义，JMM会在底层利用内存屏障。内存屏障是一种特殊的CPU指令，它能确保屏障前后的指令不会被重排序，并且能够强制将CPU缓存中的数据刷新到主内存，或从主内存重新加载数据到CPU缓存，从而保证了有序性和可见性。",
    "source": "文档中「4. JMM的内存屏障与指令重排」部分",
    "hint": "文档的关键句：“内存屏障是一种特殊的CPU指令，用于防止特定的操作被重排，保证操作的有序性。”"
  },
  {
    "question": "关于 `volatile` 和 `synchronized` 的区别，以下描述哪项是正确的？",
    "options": [
      "`volatile`能保证代码块的原子性，而`synchronized`只能保证单个变量的可见性。",
      "`volatile`是一种比`synchronized`更重的锁机制，开销更大。",
      "`synchronized`可以保证代码块的原子性和可见性，而`volatile`只能保证单个变量的可见性和有序性，不保证原子性。",
      "两者都可以互换使用，实现效果完全相同。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "这是一个关键的区别点。`synchronized`通过锁定一个对象，确保同一时间只有一个线程能执行临界区代码，从而保证了这段代码的原子性（不可分割）和可见性（执行完后结果对其他线程可见）。而`volatile`仅作用于单个变量，保证该变量的读写操作对其他线程可见，并防止相关指令重排，但它无法保证复合操作（如 i++）的原子性。",
    "source": "文档中「6. volatile的原理与内存可见性」部分",
    "hint": "在文档末尾有一个关键对比：“`volatile`只能保证单一变量的可见性，而`synchronized`则可以保证代码块的原子性。”"
  }
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            const totalQuestions = quizData.length;
            const answeredCount = userAnswers.filter(a => a !== null).length;
            const wrongCount = answeredCount - correctCount;
            const skippedCount = totalQuestions - answeredCount;
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            const errorRate = totalQuestions > 0 ? Math.round((wrongCount / totalQuestions) * 100) : 0;

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                '<h2>答题报告</h2>' +
                '<div class="score-summary">' +
                '<div class="score-card">' +
                '<h3>得分</h3>' +
                '<p>' + correctCount + ' / ' + totalQuestions + '</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>正确率</h3>' +
                '<p>' + accuracy + '%</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>错误率</h3>' +
                '<p>' + errorRate + '%</p>' +
                '</div>' +
                '<div class="score-card score-details">' +
                '<table>' +
                '<tr><td>正确</td><td>' + correctCount + '</td></tr>' +
                '<tr><td>错误</td><td>' + wrongCount + '</td></tr>' +
                '<tr><td>未答</td><td>' + skippedCount + '</td></tr>' +
                '</table>' +
                '</div>' +
                '</div>' +
                '<div class="report-actions">' +
                '<button id="review-btn">回顾测验</button>' +
                '<button class="primary" onclick="location.reload()">再试一次</button>' +
                '</div>' +
                '</div>';

            let reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  